Spark plug



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SPARK PLUG Filed Aug. '12. 1942 Il Il SM/VMW/(JVENTOR nrro/VEY v Patented Apr. 18, 1944 UNITED STATES. PATENT ortica g SPARK lPLUG Sam D. Heron and Karl Beaver, Detroit, Mich.,

assignors of one-half to Ethyl Corporation, Detroit, Mich., a corporation of Delaware, and one-half to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Claims.

This invention relates to spark plugs and particularly to plugs for use in high duty engines such as those employed in aircraft. In many spark plugs leakage of combustion gases between the core and the center electrode, or the core and the outer shell will cause failure of the plug by overheating. In many designs of radio shielded aviation spark plugs gas leakage does not have any undesirable effects as regards overheating but results in forming electrically conducting liquids or gases on the inside surfaces of the insulating material which promote a flashover across the shielding insulation.

The principal objects of our invention are to provide a spark-plug construction in which gas leakage between core and shell will not aifect the insulation within the radio shielding barrel while at the same time providing a large area of contact between the core and the shell so that gas leakage does not cause overheating and providing a method of mounting the core in the shell which minimizes stresses in the core.

In the accompanying drawing showing our preferred spark plug construction,

Fig. 1 is a side view of the spark plug;

Fig. 2 is a longitudinal sectional View of the plug:

Fig. 3 is a view, partly in longitudinal section, of another mode of forming the plug; and,

Fig. 4 is a side view of a conical metal sleeve as used in the first form of plugillustrated.

Fig. 5 is a partial sectional view showing a modined form of conical sleeve.

The spark plug shell I0 is of the one piece radio shielded airplane type having an inner threaded end I I which is screwed into the engine head up to the shoulder I2, and an outer radio shield I3 having an insulating sleeve I4. Within the shell I0 is a spark plug core I5 having a tapered portion I6 and' a cylindrical'portion Il ending about midway of the shield I3. Within the core is the central electrode I8 which coacts with the end electrode I9.

The tapered portion I6 has its largest endat the inner end of the shell so that thegas pres'- sure within the engine tends to seat the core in the shell.

The shell I0 has a complementary coned inner.

surface at 20 and between the cone and the shell is a metal sleeve 2l. This sleeve is preferably made of a metal whose annealing temperature is below the working temperature of the plug. For plugs for aviation engines I prefer to make the sleeve of silver which anneals duroperation.

the cone 2l and of the coacting surfaces is such that when the assembly is pressed together or the outer shell is shrunk onto the coned sleeve and core the angle of the cone and the friction make the unit self sustaining.

Our construction avoids the leakage of combustion gases into the shielding barrel by collecting the gases leaking between the core and the sleeve and leaking between the sleeve and the shell in grooves 23 and 24 which are vented to the atmosphere. The core may be grooved at its upper end as at 23 or a shallow groove 24 may be formed in the shell. In either case the groove communicates `with radia1 holes 22 passing through the sleeve. communicate with the groove 24 in the shell or on lthe outside of the sleeve. This groove, whether on the sleeve or in the shell communi- "cates with one or more holes 25 drilled in the shell and which serve to vent the leakage gases to atmosphere and avoids any gas pressure which will cause leakage past the remainder of the sleeve which seals the leak-off groove system from the shielding barrel.

In the form of the invention shown in Fig. 3 the grooves are omitted and the cone is made in two parts 26 and 21 separated at a point opposite the holes 25 to form an annular channel 28.' This construction avoids weakening the core or the shel1 by forming a groove in them and it is less expensive to produce.

In the forms of spark plug shown even an initial high leakage does not upset the engine In many cases the leakage' has stopped during engine operation.

While we have illustrated and described our preferred formof spark plug many variations may be made from this as by electroplating or spraying tho conical metal sleeve on to the spark plug core and by forming the sleeve thick enough so that one or more annular grooves 29, 30 Fig. 5 may be formed in it instead of on the surface of the core or shell.

We claim:

1. A spark plug having a shell tapered for a portion of its inner surface, a core having a tapered portion on its outer surface, and a metal sleeve seated between the vtapered portions of the shell and core and having a passage therethrough, the shell having a vent extending from the passage through the sleeve to the outside of the shell.

2. A spark plug having a shell tapered for a portion of its inner surface and an annular ing operation of these engines. The angle of groove in this surface, a core having@ tapered- The holes 22 also portion with an annular groove on its outer surface, and a metal sleeve seated between the tapered portions of the shell andcore and having a vent in communication with both annular grooves, the shell having a vent extending from the annular groove to the outside of the shell.

3. A spark plug having a shell tapered for a portion of its inner surface, a core having a tapered portion on its outer surface, and a metal sleeve seated between the tapered portions of the shell and core, the sleeve having annular grooves inside and out with a hole in the sleeve putting these grooves in communication, said grooves in turn are in communication with a hole in the shell which is in communication with the atmosphere outside the plug.

4. A spark plug having a shell tapered for a. portion of its inner surface and a vent extending from this surface to the outside of the shell, a core having a tapered portion on its outer surface, and a metal sleeve formed in two parts seated between the tapered portions of the shell and core, the two parts of the sleeve being separated opposite the inner end oi the vent to form an annular channel between the shell and core. 5. A spark plug having a shell tapered for a portion of its inner surface and a vent from this surface to the outside of the shell, a core having a tapered portion on its outer surface, and a metal sleeve, seated between the tapered portions of the shell and core, formed on the tapered portion of the core, the sleeve having an annular groove on its outer surface communieating with the vent in the shell.

KARL BEAVER.

SAM D. HERON. 

